A negative air ion is an atom or molecule in the air that has gained an electron, while a positive ion has lost an electron. Both positive and negative ions occur naturally in the air. However, negative ions are more concentrated in fresh air. Negative air ions can be produced by lightning, ocean surf and waterfalls. There are also electrical devices called 'air ionisers' that produce negative air ions. Such air ionisers have been used in the treatment of seasonal winter depression.
Levels of a chemical messenger in the brain called serotonin decrease in autumn and winter. This decrease may be related to the depression that some people experience in the winter months. It has been proposed that negative air ions cause an increase in brain serotonin levels.
Two well-conducted studies have looked at the effects of air ionisation on winter depression. Both of these studies compared a high-density air ioniser with a low-density ioniser. People sat in a room at home with the ioniser for 30 minutes every morning over a 2-3-week period. People with winter depression who used the high-density ioniser showed much more improvement than those who used the low-density ioniser. No studies have been carried out on air ionisation as a treatment for other types of depression.
No side effects of air ionisation have been found. However, air ionisers are expensive to buy.
Air ionizers are available from electronics stores and can be bought on the internet. It is important to check the technical specifications of any air ioniser. Some of those on sale do not produce a high density of negative ions. A high-density ioniser produces 2,700,000 ions per cubic centimeter, while a low-density one produces only 10,000 ions per cubic centimeter.
Air ionisation appears to be a promising treatment for winter depression, but more research is needed. Research still has to be carried out on its use with other types of depression.
Last reviewed and updated: 1 February 2006